The present invention relates generally to the area of fluid applicators and more particularly to a fluid applicator with a noncontacting die for fiberizing a flat fluid stream and applying the fiberized fluid stream as thin coating strip with sharply defined uniform edges on a substrate.
Hot melt thermal plastic adhesives have been widely used in industry for adhering many types of products and are particularly useful in applications where quick setting time is advantageous. Further, in many applications, the adhesive must be sufficiently thinly applied so that its presence is not apparent on the opposite side of the substrate. In those applications several different designs of fluid applicators have been developed. For example, the adhesive may be dispensed as a straight adhesive bead which is then swirled by air passing through air jets circumferentially spaced around the adhesive bead. An applicator of that type is disclosed in U.S. Pat. No. Re. 33,481 issued to the assignee of the present invention. Fluid applicators may also contain contacting dies which are effective to spread extruded streams of adhesive in predetermined patterns across a substrate. An example of a contacting die is disclosed in U.S. Pat. No. 4,687,137 also owned by the assignee of the present invention.
More recent applicators are of a noncontacting die design, an example of which is disclosed in U.S. patent application Ser. No. 07/910,784 which is assigned to the same assignee as the present application. The die includes an adhesive dispensing die with a dispensing zone, or slot, terminating at a dispensing die outlet. The die further includes fiberizing air dies mounted to the die to form fiberizing slots arranged adjacent to and on each side of the dispensing die outlet. The slotted die extrudes a continuous flat stream of hot melt adhesive through the dispensing die slot. Simultaneously therewith, hot air is dispensed through the adjacent fiberizing die slots. The hot air impinges upon and tears or separates the continuous flat stream of extruded adhesive into a discontinuous or fiberized stream of hot melt adhesive. The fiberized adhesive stream is then applied as a thin uniform coating on a substrate. The fiberizing air may be activated, or turned on, in each fiberizing slot in any combination with the adhesive dispensing cycle to obtain the desired shape and spread or control of the fiberized adhesive stream to be applied as a thin coat to the substrate.
The above described die set includes a pair of dispensing dies which are joined together with a dispensing shim therebetween to form the dispensing die slot through which the adhesive is dispensed. Each of a pair of fiberizing dies is attached to a respective one of the dispensing dies. Each fiberizing die has two surfaces which intersect to form a corner of the fiberizing die and which interface with two surfaces on its respective dispensing die. The dispensing and fiberizing dies have opposed first surfaces with intersecting air passages to connect a source of pressurized air passing through the dispensing die to the fiberizing die slots. In addition, the air and dispensing dies have opposed second surfaces that are operably connected to form the fiberizing slots terminating at a fiberizing die outlet on each side of the dispensing die outlet. The second surface of the fiberizing die has orifices connected to the air passages for porting the pressurized air into the fiberizing die slot and out the fiberizing die outlet.
As disclosed in the above referenced patent application, the fiberizing dies contain precision machined bosses which bear against interfacing surfaces of the dispensing dies to define the fiberizing die slot. Such a construction relies on metal to metal contact to form the required air seal which is difficult and expensive to manufacture and requires a different fiberizing die in order to change the size of the fiberizing die slot. In addition, the fiberizing air is typically routed through the fiberizing dies and enters a wide groove or cavity formed in the first surfaces of the fiberizing dies. The air cavity extends around a corner edge of the dies and across the second surfaces of the fiberizing dies such that the air cavity is contiguous with the fiberizing slots. Consequently, the handling of the pressurized air in a slotted die set is particularly complex and requires fiberizing die components which are difficult and expensive to manufacture.
The fiberizing dies of the above described slotted die set are clamped to the dispensing dies using a single screw or fastener at each end of the die set. Those screws are effective to provide the desired clamping forces at the ends of the dies, but the clamping forces diminish in proportion to the distance moved away from the ends of the die set. For example, at the midpoint of the die set, the clamping forces on the metal-to-metal contacts between the fiberizing and dispensing dies may be insufficient to provide reliable air seals.
In the above described noncontacting slotted die set, a slotted dispensing shim is located between opposed surfaces of the dispensing dies. The dispensing shim has a longitudinal member which extends the full length of the die outlet. The slotted dispensing shim further includes downward projecting tabs that extend to the die outlet. The slotted dispensing shim in combination with the opposed surfaces of the dispensing dies form the dispensing slots through which the adhesive is discharged. The shim tabs have straight sides which terminate into pointed ends. The straight sides of the tabs are effective to provide coating edges which are sharp and clean; however, when using multi-zone die sets, it is desirable to have the ability to adjust the location of adjacent coating edges.
Many coating applications require that the pressurized air discharged with the adhesive stream be heated. Typically, air is heated on the applicator by passing ambient air through a heater comprised of a generally rectangular manifold which has cartridge heaters extending its full length. The manifold further has air passages drilled both along its length and width which are connected in a desired pattern such that the proper heat exchange takes place as the air moves through the manifold. During the manufacture of the heater it is necessary to seal openings in the surfaces of the heater which were created by drilling the required passages. Typically, 20 to 30 such holes must be filled. Those holes are most often plugged with a commercial plug sold for that purpose. However, such plugs generally require precise machining and special assembly tooling. Further, it is possible that in the manufacturing process, a hole may not be plugged, a wrong hole may be plugged or a hole may be plugged improperly. Further, if the heater requires internal cleaning, removal and replacement of the plugs is time consuming and expensive. Therefore, a heat exchanger of the above construction is relatively expensive to manufacture, difficult to maintain, and may be the source of an inadvertent manufacturing error or unreliable operation.
Different adhesive dispensing processes, for example, straight bead dispensing, swirled bead dispensing and flat stream dispensing have the same general fluid control process. Hot melt adhesive is received by an adhesive manifold from a source; is channeled to a pump attached to the manifold; the pump output is connected to the manifold; and the pump output is distributed within the manifold to either a supply plate or a return plate depending on the applicator operation. From the supply plate, fluid flow is controlled by valves which direct the fluid to dispensing mechanisms. The return plate also has valves mounted thereon the outputs of which merge the fluid flow into a single return line which exits the return plate. However, each different dispensing process uses an adhesive manifold, and supply and return plates that have different adhesive routings which require different patterns of porting interfaces between the adhesive manifold and the supply and return plates. Therefore, it is necessary to use a different set of manifold and supply and return plates for each different dispensing process.